Your local government (council) should be able to advise you on this.
Alternatively and probably better - consult your old high school chemistry
books and see if there is something you can mix with it to turn it into
something useful like Ammonium Sulphate which can be used as a fertiliser on
your plants. Any precipitated copper can then also be used as a trace
element. :)

That's what I do for the small quantity I use. Although it would be
best to save it up and dispose of it at your local council chemical
cleanup day (if you have one). We had ours the other week and it was so
popular that there was an hour long wait to get in!

After using ferric chloride as a kid and hearing talk about not pouring
it down the sink, it was interesting to find out that Sydney Water
actually add it to our drinking water! Not that I drink tap water
anyway :->

I stored it in a soft drink bottle, and after a few months, it evolved
enough gas to burst the bottle, and etchant went everywhere. I have
pressurised those softdrink bottles to more than 150PSI without them
bursting, so I hate to think how much pressure was in there when it did
burst. To add to the embarrassment, it happened whilst we had guests
staying over. I had labelled the bottle with lots of stickers saying
"Toxic", so I don't think they were amused when it went everywhere.

You could always evaporate it, and end up with crystals mostly of copper
sulphate and a bit of ammonium sulphate (if you've used the etchant a
lot). I have a few jars of big blue copper sulphate crystals as a result.

This stuff is excellent for discouraging termites. Mix copper sulphate with
an equal
quantity of calcium carbonate (crushed limestone) and mix with water (100g per
litre),
pour it in small quantities (100ml per tree) round the base of your favourite
trees and
termites will not trouble for at least a couple of years.